||Polyketone is a thermoplastic polymer with excellent chemical and physical stability. Because of its excellent stability, it is not easy to attach it functional groups to PK chain, thus many studies are under way. In this study, polyketone cation exchange membranes were prepared by direct sulfonation reaction of polyketones with chlorosulfonic acid. FT-IR, elemental analysis, SEM and XPS analysis were carried out to confirm the structure of polyketone membrane with cation exchanger. Also, basic properties such as water uptake, swelling ratio, ion exchange capacity and electrical resistance were measured.